Modern aircraft have various electrical systems that require different types of power. Some loads might require 28 VDC power like the cabins of the aircraft for general lighting systems. The low voltage DC power might also be used for aircrafts display monitors in the cockpit for presenting fight information while some may be used for providing power to entertainment displays during flight. In addition to the low voltage 28 VDC system loads will be loads that require large power such as galleys and these would be powered by 115 VAC power. Another AC 115 V load might be a backup electric fuel pump used in case a gear driven fuel pump fails. Many of these systems on today's aircraft are electrically controlled and therefore required electrical operating power.
Some of the electrical system loads on an aircraft are deemed essential, while other electrical system loads might be deemed non-essential. Examples of essential system loads are the systems that are employed to keep a plane flying in a controlled manner. Some of the electrical system loads, such as, perhaps, an entertainment system, might be considered non-essential. Essential system loads are generally electrically separated from non-essential system loads so that if the power supplied by an aircraft's generator is limited, such power can be directed to essential system loads first. Electrical system loads are also separated to prevent a common mode or same failure type cannot disable both the essential and non-essential system loads with a single electrical fault. To address these needs, aircrafts have power-distribution systems for controlling the supply of power to the various circuits and systems requiring electrical power.
Aircraft electric power distribution systems are generally segregated into three channels of electric supply power for redundancy and safety. The two main channels of electric power are segregated right and left on the aircraft and an emergency electric power channel is further isolated as a final source of power in an emergency. A typical main channel of an aircraft electric power system will consist of an AC 115 VAC distribution panel and a 28 VDC distribution panel. Each of these panels control, protect and distribute the electric power to the aircraft.